2023 AMC 12A Problems/Problem 7

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Problem

Janet rolls a standard $6$-sided die $4$ times and keeps a running total of the numbers she rolls. What is the probability that at some point, her running total will equal $3$?

Solution 1

There are $4$ cases where her running total can equal $3$: 1. She rolled $1$ for three times consecutively from the beginning. Probability: $frac{1}{6^3} = frac{1}{216} 2.  She rolled a$1$, then$2$. Probability:$frac{1}{6^2} = frac{1}{36} 3. She rolled a $2$, then $1$. Probability: $frac{1}{6^2} = frac{1}{36} 4.  She rolled a$3$at the beginning. Probability:$frac{1}{6}

Add them together to get $\boxed{textbf{(B)} frac{49}{216}}$